1. Field of the Invention
The present invention relates to sensors which can be used to activate or otherwise control vehicle safety systems. More specifically, the present invention relates to an optical sensor which can discriminate between objects based upon range from the sensor.
2. Technical Background
Vehicle safety is a significant concern to consumers and manufacturers alike. A number of features have been designed which make automobiles safer to operate. Some of the earliest features designed to make vehicles safer are devices designed to protect the vehicles and their occupants from impact. These devices are passive in nature requiring no action from the driver to activate them. Such safety features include bumpers and reinforced body panels and vehicle frame.
As the design of vehicles has advanced, so have the number and complexity of their safety features. The advent of the seatbelt was a significant advancement in vehicle safety. Seatbelts are generally an active restraint device, requiring the vehicle occupant to correctly fasten and tighten the seatbelt. When seatbelts are properly worn, an occupant's injuries in a crash are generally less severe. Moreover, the seatbelt may assist a driver in avoiding a crash by holding the driver behind the vehicle controls during evasive maneuvering.
Another significant advancement in vehicle safety is the inflatable cushion or airbag. Airbags have become standard equipment on most vehicles sold in the United States, and their installation is required by law for most new vehicles. Airbag modules commonly contain a collision sensor, an inflator, and an airbag cushion. In the event of an accident, a collision sensor such as an accelerometer, measures abnormal deceleration and triggers the inflator by means of an electronic signal. The inflator is generally a pyrotechnic device which produces pressurized gas. The inflator is connected to the airbag cushion and inflates the airbag cushion through an opening in the airbag cushion.
Prior to inflation, the airbag cushions are housed in an uninflated and folded condition to minimize space requirements. Typically the airbag module is housed in the steering wheel on the driver's side of a vehicle and in the dashboard on the passenger side of a vehicle. Upon receipt of the signal from the collision sensor, the inflator rapidly produces a quantity of inflation fluid or gas which inflates the cushion and protects the passenger from harmful impact with the interior of the car.
Unlike seatbelts which require active effort from the occupant to protect, airbags are passive requiring no action on the part of the occupant. Because the airbag is passive, the sensor must be able to detect or anticipate a crash. Thus, in a fraction of a second, a sensor must detect the rapid change in acceleration and send a signal to the inflator to inflate. Generally, this detection begins after the vehicle has already impacted the object.
Airbag cushions are generally installed in the front seating area of a vehicle to protect the driver and passenger from impact with the windshield, the steering column, and the instrument panel. The inflating airbag cushions protect an occupant by rapidly inflating. The force of the inflation must be sufficiently strong to counteract the force of the occupant being thrown forward. Accordingly the larger the occupant, the stronger the force required to protect the occupant.
Because adults are the most common occupants of the front seats, many airbag cushions have been designed to inflate with a force to protect the typical adult. However, the actual occupant may be much larger or smaller than the typical adult. Thus, if a child or small adult is seated in the front seat the force of the inflating airbag may be too large for optimal protection. Likewise if a large person is seated in the front seat the force of the inflating airbag may be insufficient for optimal protection of the occupant.
Recently, “smart” airbags have been developed that can inflate with a variable force depending on the mass of the occupant to be protected. Thus, such smart airbags can be configured to inflate with the appropriate force to optimally protect the actual occupant of a front seat. Key to this proper inflation is the detection of the size of the occupant in the seat. Currently available detectors may use a sensor to detect the weight of the person in the seat. However, such sensors may not take into account such factors that may add to weight detected, such as a child safety seat, without indicating the actual size of the occupant.
Seatbelts and airbag cushions are generally designed to protect occupants of a vehicle from an impact. Other Safety systems have been designed which can assist a driver in avoiding an impact, or protect occupants of another vehicle from an impact. Such devices include warning systems that indicate that an object is close to the front, side, rear of a vehicle. Thus a driver may be assisted in avoiding a pedestrian, a vehicle, or another object.
Other safety devices may be designed to lessen the impact to another vehicle or damage to the subject vehicle. One such device is a configured to dip the nose of the car prior to an impact. Such dipping, particularly when installed on a vehicle with high ground clearance, may assist the vehicles in aligning bumpers and prevent damage to the smaller vehicle caused by the bumper of the large vehicle.
Airbags and these newer safety devices all require a sensor that can detect a crash sufficiently early to allow for activation of the safety feature. In some cases the nature of the device dictates that the sensor detects the crash before it actually occurs. In yet other instances, such as lane change and back-up warning systems, the sensor must detect the mere possibility of an accident and warn the driver of the risk of a collision.
Recently, optical sensors or vision systems have been developed to rapidly detect a collision. Additionally, such optical sensors can also be used to assess the risk of a collision and warn the driver to take appropriate measures.
For a vision system to function properly, it must be able to discriminate between objects near the sensor and objects further away. If an optical sensor cannot discriminate based on the range of the object, objects that are distant from the sensor may be determined to be important causing the sensor to give a false positive result. Vision systems that can discriminate on the basis of range from the sensor are commonly made in two ways. The first is the use of stereo cameras. With two cameras, the disparity measurements between the two images in the two cameras can be used to determine the distance from the sensor. Because this system uses two cameras and electronic image processing elements, the cost of manufacture can be relatively high. Additionally, the risk of system malfunction is also increased.
The second way commonly used in vision systems to discriminate based on range uses one camera. The sensor uses structured or structurless light added to the image in a controlled way. Such light can be emitted by a light source adjacent the sensor. The light is then reflected off an object of interest and then detected by the camera. By analyzing the size and other characteristics of the reflected light, the sensor can determine the distance of the object. Because this system requires the use of some type of light projector, the cost of the system may also be quite high. Additionally, the projection and reflection of light may not function adequately in direct sunlight and with certain types of surfaces.
Accordingly, a need exists for a sensor which can rapidly detect an immient vehicle impact and activate a vehicle safety feature. It would be an additional advancement in the art to provide a sensor which can assess the risk of an impact prior to an accident. It would be a further benefit if the sensor could discriminate between object based upon the distance from the sensor. It would be an additional advancement to present an optical sensor which could detect the distance from the sensor while using a single digital camera. It would be further benefit if the optical sensor would function without the addition of light. It would be an additional advancement to provide a sensor that could discriminate between an occupant of a front seat and an occupant of a rear seat of a vehicle.